From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: Can we increase vring size over 1024? Date: Fri, 2 Sep 2016 20:32:36 +0300 Message-ID: <20160902201909-mutt-send-email-mst@kernel.org> References: <33183CC9F5247A488A2544077AF19020B03B318E@SZXEMA503-MBS.china.huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "stefanha@redhat.com" , "jasowang@redhat.com" , "kvm@vger.kernel.org" , "virtio-dev@lists.oasis-open.org" , "qemu-devel@nongnu.org" , "Lilijun (Jerry)" , "Huangpeng (Peter)" To: "Gonglei (Arei)" Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Content-Disposition: inline In-Reply-To: <33183CC9F5247A488A2544077AF19020B03B318E@SZXEMA503-MBS.china.huawei.com> List-Id: kvm.vger.kernel.org On Fri, Sep 02, 2016 at 06:55:35AM +0000, Gonglei (Arei) wrote: > Hi Michael & all, > > Michael, you made a presentation about the virto 1.1's new features in KVM Forum last week. > That's wonderful! > > And I'd like to know can we increase vring size over 1024, such as 4096 or 8192? > > My colleage had asked the same question in 2014, but she didn't get a definite answare, > So, I want to rewake up the dissusstion about this. Becase for the virtio-crypto device, > I also need to increase the vring size to get better performance and thoughput, but the Qemu > side limit the thought as VIRTQUEUE_MAX_SIZE is 1024. > > [QA-virtio]:Why vring size is limited to 1024? > http://qemu.11.n7.nabble.com/QA-virtio-Why-vring-size-is-limited-to-1024-td292450.html > > Avi Kivity said that google cloud exposed the vring size to 16k. > > Regards, > -Gonglei Fundamentally, the reason is that the ring size currently also sets the max s/g list length, and linux hosts can't support bigger lists. We should fix that in 1.1. -- MST